# It would be interesting to see the color chosen by children to draw water in a culture that doesn’t have this habit. I think that we identify water as blue because we know about the oceans, and we have aerial photography and very clean swimming pools. But few cultures had those things until recently. Are there enough hints that they would unconsciously color it blue? Or is that entirely a learned habit?
** Although astronomers haven’t always believed that it’s the majesty of the cosmos they’re looking at. In 1964, Robert Wilson and Arno Penzias detected waves from the sky at microwave wavelengths that shouldn’t have been there. They spent a long time trying to work out which bit of the sky or their telescope was messing up the measurement, sure that something was generating extra microwave light. They also cleared out some nesting pigeons from the telescope, along with their droppings (euphemistically described as “white dielectric material” in the paper they wrote). The unwanted background light persisted. It eventually turned out to be the signature of the Big Bang, some of the most ancient light in the universe. There is something special about an experiment that has to be very careful to distinguish between the aftereffects of pigeon poop and the aftereffects of the formation of the universe.
?? Which has very little to do with how a real greenhouse does anything.
?? That’s why mobile phones are called cell phones in US English—the network is cellular.
CHAPTER 6
Why Don’t Ducks
Get Cold Feet?
SALT IS OFTEN considered a mundane commodity, stored away in cupboards, never the center of attention. But if you look a little bit more closely at a handful of grains of salt, especially in bright light, you’ll notice that it’s surprisingly sparkly. And it gets better as you get closer. Peer at it through a magnifying glass, and you’ll see that the grains aren’t randomly shaped, or lumpy, or rough. Each one is a beautiful little cube with very flat sides, perhaps 0.02 inch across. This is why it sparkles; light is reflecting off those flat faces as though they were tiny mirrors, and different salt grains are glinting at you as you turn the pile in the light. The boring stuff in the salt cellar is made up of minuscule sculptures, each with the same precise shape. Salt manufacturers don’t do this deliberately—it’s just how salt forms. And it gives us a clue about what “stuff” is made of.
Salt is sodium chloride, and it’s made of equal numbers of sodium and chloride ions.* You can think of them as balls of different sizes—the chloride has almost twice the diameter of the sodium. When salt is forming, each one of its components has a fixed place in a very specific structure. Like eggs in a stack of giant egg cartons, the chloride ions assemble in rows and columns, so that they sit on a square grid. The smaller sodium ions fit into the spaces in between, so that each little box of eight chloride ions has a sodium ion in the middle. A salt crystal is just a giant grid like this, a cube that’s a million or so atoms long on each side. When the salt crystals grow, they tend to grow a new layer across an entire flat face before they start on the next layer, so the cube keeps its flat sides as it grows. It’s atomic-scale filing, each component stacked up perfectly in its place. And the flat sides of each cube can reflect light like a mirror.
We can’t see the individual atoms, but we can see the pattern of their structure because the whole salt crystal is just that same pattern repeated again and again. Salt is very simple, and a bigger salt grain is just more of the same. The flat faces that make the salt sparkle are there because individual atoms have to sit in specific places on a rigid lattice.
Sugar also sparkles, but when you look more closely at sugar crystals (especially the larger ones, like those in granulated sugar), you’ll see something even more beautiful. These crystals are six-sided pillars with pointy ends. Each sugar molecule is made up of forty-five different atoms, but those atoms are held together in a fixed way that is the same in each individual molecule. One sugar molecule is a brick in a crystalline sculpture, even though it’s a brick with quite a complicated shape. Like the simpler salt crystals, these too stack up on top of each other in a regular lattice, and there’s only one pattern for them to follow. Once again, we can’t see the atoms, but we can see the pattern because the whole crystal is just a giant stack, a skyscraper of molecules. Since the six-sided pillars have flat sides that can act as mirrors, sugar sparkles just like salt.
Flour and rice and ground spices don’t sparkle, because they have a much more complicated structure—they’re made from the tiny living factories that we call cells. The only reason sugar and salt crystals have perfectly flat sides is that they have such a simple structure: just rows and columns of atoms slotted into specific positions. And that perfect repetition is only possible because at the bottom of it all there are billions of tiny identical building blocks: atoms. The sparkling is a reminder of their existence every time you put a spoonful of sugar in your tea.
Even though we can’t see the atoms themselves, we can see the consequences of what’s happening down there in the world of the tiny. The goings-on at the bottom of the size scale directly affect what we can do at the largest scales in our society. But first, you have to believe that atoms exist.